1. Field of the Invention
The present invention relates to a vertical diffusion bonding apparatus, and particularly to a vertical diffusion bonding apparatus serving as a preferred apparatus for diffusion-bonding metal pipes, such as oil well tubes for drilling, tubing or casings disposed vertically.
2. Description of the Related Art
In a diffusion bonding method, bonding members to be bonded to each other are held in close contact with each other, and pressed to a degree which does not cause plastic deformation, so that the bonding members are bonded by using diffusion of atoms which takes place in the interface between the bonded surfaces.
The diffusion bonding method, the solid-phase diffusion bonding method and a liquid-phase diffusion bonding method are known. In a solid-phase diffusion bonding method, members to be bonded are brought into direct and close contact with each other to cause atom elements to be diffused while the solid state is maintained. In the liquid-phase diffusion bonding method, an insertion material having a low melting point is inserted into a space between the members, and then, the insertion member is temporarily melted to cause dissipation of specific elements in the liquid phase in the member and isothermal solidification to occur to bond the members to each other.
The diffusion bonding method is different from the mechanical bonding method, such as a bolt fixing method and a rivet bonding method, in that saving of materials and reduction in the number of man-hours are obtained. Moreover, bonding exhibiting satisfactory bonding strength, airtightness, pressure resistance and the like can be obtained. In addition, the time required to produce each bonding is shorter than time required for the welding method. Since the above-mentioned advantages can be obtained, the diffusion bonding method has been widely used as a method of bonding oil well tubes for drilling oil, anti-corrosion pipes for use in the chemical industry, line pipes for transporting crude oil and elongated stainless steel pipes for use in seawater heat exchangers.
Usually oil wells exist at positions thousands of meters underground. Therefore, when oil well tubes are embedded underground, metal pipes each having a length of 10 meters to 15 meters must sequentially be bonded to one another, and then moved downwards in a vertical hole formed underground. A vertical diffusion bonding apparatus has been employed to diffusion-bond the oil well tubes to one another, the apparatus being arranged to dispose metal pipes in the vertical direction and perform diffusion bonding while supplying the metal pipes from an upper position to the lower position.
Many types of vertical diffusion bonding apparatuses have been suggested. For example, one diffusion bonding apparatus has been suggested in EP 0 882 539 A2. The apparatus incorporates a lower block for holding a lower pipe member and an upper block for holding an upper pipe member and pressing the held upper pipe member against the lower pipe member. In the apparatus, an elevating member for holding the upper pipe member is moved downwards by using three or more hydraulic cylinders so as to press the upper pipe member against the lower pipe member.
FIG. 9 is a schematic view showing a vertical diffusion bonding apparatus having a structure similar to prior art diffusion bonding apparatus. Referring to FIG. 9, the vertical diffusion bonding apparatus 10 is provided with a lower block 14, an upper block 16, a pressurizing mechanism 18 and a heating mechanism 20.
The lower block 14 is secured to the lower portions of four frames 18a. Two lower clamping mechanisms 14a and 14b disposed apart from each other for a predetermined distance are provided on the lower block 14. A metal pipe (a lower pipe member) 22a disposed at a lower position is held at two positions.
The upper block 16 can move vertically in the perpendicular direction because the upper block 16 is slidably disposed above the frames 18a through sliders 16c. Two upper clamping mechanism 16a and 16b disposed apart from each other for a predetermined distance are provided for the upper block 16 so that a metal pipe (an upper pipe member) 22b supplied from an upper position is held at two positions.
The pressurizing mechanism 18 has four frames 18a, a main beam 18b, a holding beam (not shown) secured to the main beam 18b and three pressurizing cylinders 18c. The three pressurizing cylinders 18c are disposed at angular intervals of about 120.degree. to surround the metal pipe 22b. The ends of the pressurizing cylinders 18c are secured to the holding frame (not shown), while the other ends are secured to the upper block 16.
The heating mechanism 20 has a two-piece heating coil 20a for induction-heating an area in the vicinity of the interface between the metal pipes 22a and 22b to be bonded; and two-piece shield chamber 20b for maintaining a predetermined atmosphere in the vicinity of the foregoing interface. Wheels 18d are disposed at the lower ends of the frames 18a. Thus, the overall body of the vertical diffusion bonding apparatus 10 is able to move forwards/rearwards along rails 24a provided for a base frame 24.
The metal pipe 22a and 22b are diffusion-bonded to each other by using the vertical diffusion bonding apparatus 10 shown in FIG. 9 in accordance with the following procedure. As shown in FIG. 10A, which is a side view, the vertical diffusion bonding apparatus 10 is retracted rearwards (in the right-hand direction in FIG. 10A) along the rails 24a provided on the base frame 24. The metal pipe 22a held by a tube clamp 26 is moved downwards by using a crane 28 and held by a tube clamp 30 secured to the base frame 24.
Then, as shown in FIG. 10B, the tube clamp 26 which was holding the metal pipe 22a is released, and then the tube clamp 26 is secured to the other metal pipe 22b that is to be bonded to the metal pipe 22a. Then, the crane 28 (not shown in FIG. 10B) is operated to move the metal pipe 22b to a position above the metal pipe 22a.
At this time, the metal pipe 22a and the metal pipe 22b are not brought into contact with each other, that is, they are separated from each other by a predetermined distance. As shown in FIG. 10C, the metal pipes 22a and 22b are moved to the central portion of the vertical diffusion bonding apparatus 10 by moving the vertical diffusion bonding apparatus 10 forwardly along the rails 24a (in the left-hand direction in FIG. 10C).
Then, as shown in FIG. 11A which is a front view, the lower clamping mechanism 14a and 14b provided for the lower block 14 is secured to the metal pipe 22a. Also, the upper clamping mechanism 16a and 16b provided by the upper block 16 holds the metal pipe 22b at an upper position. Then the tube clamp 26 is released. If an end surface of the metal pipe 22a or the metal pipe 22b has a flaw, such as a nick, an end-surface finishing machine 32 associated with the vertical diffusion bonding apparatus 10 may be operated to flatten the end surface of the metal pipe 22a or the metal pipe 22b.
Then, as shown in FIG. 11B, the pressurizing cylinders 18c are operated to press the metal pipe 22b against the metal pipe 22a. Then, the two-piece heating coil 20a is moved to a position adjacent to the interface between the surfaces to be bonded, and then the portion in the vicinity of the interface between the bonded surfaces is covered with the shield chamber 20b. Then, a purging operation using inert gas is performed. Moreover, high frequency waves are applied to the heating coil 20a so as to heat the interface between the surfaces to be bonded to a predetermined temperature. Thus, the metal pipes 22a and 22b are diffusion-bonded.
After a predetermined time has elapsed and thus the temperature of the interface between the bonded surfaces has been sufficiently lowered, the shield chamber 20b and the heating coil 20a are removed. Then, the lower clamping mechanism 14a and 14b and the upper clamping mechanism 16a and 16b are released.
As shown in FIG. 11C which is a side view, the vertical diffusion bonding apparatus 10 is retracted rearwards (in the right-hand direction in FIG. 11C). Moreover, the tube clamp 26 is again secured to the upper portion of the metal pipe metal pipe 22b. Then, the tube clamp 30 of the base frame 24 is released. Then, the crane 28 is operated to downwardly move the metal pipe 22b to a predetermined position, and then the metal pipe 22b is secured by using the tube clamp 30.
Thus, one cycle of the bonding operation is completed. When the processes shown in FIGS. 10A to 11C are sequentially repeated, a metal pipe having a length of thousands of meters can be embedded underground.
However, the vertical diffusion bonding apparatus 10 shown in FIG. 9 has the structure that the lower metal pipe 22a and the metal pipe 22b which is supplied from an upper position are held by the lower clamping mechanism 14a and 14b and the upper clamping mechanism 16a and 16b. Therefore, there arises a problem in that the overall structure of the vertical diffusion bonding apparatus 10 becomes somewhat complicated.
Moreover, the metal pipe 22b, which is supplied from an upper position, is secured by the upper clamping mechanism 16a and 16b, and then is abutted against the lower metal pipe 22a. Therefore, if the axes of the metal pipe 22a and the metal pipe 22b are slightly deviated from each other in the horizontal direction, the overall body of the upper block 16 must be moved horizontally. Thus, there arises a problem in that a somewhat complicated adjustment operations are required.
If the axes of the metal pipe 22a and the metal pipe 22b are slightly inclined from each other, the interface between the bonded surfaces are not in uniform contact. In this case, a uniform bonding pressure cannot be applied to the overall interface between the surfaces to be bonded. To prevent the above-mentioned undesirable state, the overall inclination of the upper block 16 for holding the metal pipe 22b located at the upper position must be adjusted. Thus, there arises a problem in that a somewhat complicated adjustment operation is required.